My advice (of course your mileage may vary):
Don't do too much planning etc. before you start, as the school will have their own way of doing things and it might be a wasted effort. But it would be good to do some getting-to-know-you stuff for the beginning of the year - especially as you probably won't get to meet the class this year. If you're itching to do things, read lots of children's books, and revise grammar terms and maths methods. Brush up on whatever foreign language they teach. You do not HAVE to do any of these, but I know I just wanted to do something, and these I think are the most likely to be useful.
Get to know the national curriculum in these year groups. If you can, find out what the planning, teaching, marking, behaviour and calculation policies are in the school. Also if the school produce a yearly overview of topics. Also if possible, ask to be put in touch with your co-teacher (if it's multi-form-entry).
When you get a year group, also ask to be put in contact with the current teacher of that class so you can pick their brains, and get details of any SEND or particular behaviours which you can have strategies for straight away. I think this would be especially useful this year as it would be good to know what they have missed out on.
Get a good storybook to read with them from the beginning of the year. If nothing else you have something to do if you run out of getting-to-know-yous!
If it's your bag, there are good facebook groups for Y3-4 or Year 5-6 teachers. Great for book recommendations especially.
I love Year 4 and 5. Year 4 can be a bit 'the Y9 of primary school', with a lot of emotional stuff as they're growing up - sometimes in different directions from their friends. Year 5 is my perfect year! Old enough, not too old. Both I think are good years to NQT in.